Modern mobile devices are often capable of communicating in both a wireless local area network (WLAN) environment and a third generation (3G) cellular telephone network environment. In a WLAN, the mobile devices can exchange data in various forms with each other using standard protocols, such as the IEEE 802.11b specification, etc. The mobile devices can also access other communication networks, such as the Internet, via the 3G cellular network over TCP/IP. A particular mobile device is usually assigned a home address (e.g., an IP address, etc.) by a home network, where the mobile device is originally registered, to be used in communication with other parties.
However, as the mobile device moves across different remote networks that are outside the home network, the different remote networks may assign different IP addresses to the mobile device. On the other hand, other parties communicating with the mobile device may still try to communicate with the mobile device based on the home address. Thus, the roaming mobile device may be unable to continue communicating with the other parties when moving across different remote networks. Techniques such as mobile internet protocol (MIP) attempt to manage the mobility of the mobile device by using a home agent and a foreign agent. The home agent receives all communications to the mobile device at the mobile device's original home IP address and forwards the received communications to the foreign agent in the remote networks across which the mobile device moves. The mobile device can then obtain the forwarded communications from the foreign agent.
However, because all communications must be received and forwarded by the home agent as a relay point, delays may occur in the communication between the mobile device and the other parties. Such delay may be large when the mobile device moves into a remote network having a long routing path to the home network. In addition, the delay may also be inconsistent due to different routing paths from the remote networks to the home network. Therefore, conventional techniques such as MIP may be undesirable for real-time applications, such as voice over IP (VoIP) applications.
Session initiation protocol (SIP) may also be used to manage mobility. SIP may manage real-time sessions directly from the mobile device by inviting other parties to start a session or sessions for communication. When the mobile device roams into a different remote network and detects a change of the IP address of the mobile device, the mobile device may re-invite other parties to start a different session or sessions to continue the communication with the changed IP address.
However, when using SIP, the mobile device often needs to determine, by frequent polling, whether its IP address has been changed. Less frequent polling may cause larger delays in re-inviting the other parties to use a different address. However, more frequent polling can increase the burden on the computational resources of the mobile device. Further, simultaneous mobility, when both communication parties are roaming, may often cause loss of established sessions or failure to establish new sessions using SIP.
Methods and systems consistent with certain features of the disclosed embodiments are directed to solving one or more of the problems set forth above.